Mechanistic insight into the Fe-atom-pairs for breaking the scaling relation in ORR

Dual-atom catalysts (DACs) show great potential for efficiently regulating multiple reaction pathways and well understanding of the fundamental mechanisms, therefore are expected to break the limitations of single-atom catalysts (SACs) in heterogeneous catalysis. Herein, Fe-DAs/NC with Fe2-N6 moieties was successfully synthesized by pyrolysis of nano-confined Fe-ZIF-8, and further employed as alkaline oxygen reduction reaction (ORR) catalyst. We propose that the two adjacent Fe atoms of Fe2-N6 moiety in Fe-DAs/NC can cooperatively bond the O2 molecule via a dual-side adsorption to boost the initial O2 adsorption and O-O dissociation, meanwhile the individual Fe atom in Fe2-N6 moiety with decreased d-band center can further break the energy barrier limit for efficient desorption of the final OH* intermediate. Due to the synergistic effect of Fe2-N6 moiety, the ORR performances of Fe-DAs/NC were fully improved compared to the single-atom Fe-N4 catalyst. Specifically, Fe-DAs/NC displays a large half-wave potential of 0.93 V, fast kinetics, high selectivity, and robust stability. And, Fe-DAs/NC-based Zn-air battery shows superior specific capacity, power density, and cycle stability than the commercial Pt/C. Our findings pave the way for rational design of atomically dispersed catalysts and afford an intensive understanding of the relationship between the structure and catalytic mechanism at the atomic scale.